1879.] J- 1 -L [Derby. 



black. The rock consists of clay, mixed with a considerable proportion of 

 finely-divided rnica and sand, the last often forming independent layers, 

 a few inches thick. The only fossils found in these shales were Fucoids, of 

 the genus Spirophyton, and small fruit-like bodies, resembling very much 

 a flattened currant, consisting apparently of a thin pellicle enclosing two to 

 six small grains. The Spirophytons are apparently identical with those de- 

 scribed by Prof. Hall, from the Hamilton group of New York. They occur 

 abundantly in all the localities, in both the black and red shale, near the 

 junction of the two. 



On the Curua and Maecuru the red shale, which is undoubtedly Devon- 

 ian, is followed by beds of coarse sandstone which, according to Mr. Smith, 

 are at least fifty feet thick on the Curua. This is followed by fossiliferous 

 Carboniferous beds. The red shale is also overlaid by coarse sandstone, in 

 the mountains of Ereie, but it is not certain that this sandstone is of the 

 same formation as that of the Curua. 



As regards the extension of the Devonian series, it has been recognized 

 as far west as the river Uatuma, a small river between the Trombetas and 

 the Rio Negro. On the southern side of the valley, there are, on the 

 Tapajos, shales containing SpiropJiyton and calcareous concretions, which 

 were referred provisionally to the Carboniferous by Prof. Hartt, but which 

 seem to me to be Devonian, and I refer to the same age the black shale 

 found by Snr. Penna on the Xingu. 



Of all the Palreozoic deposits of the Amazonas, those of the Carbonifer- 

 ous occupy the most extensive area and, at the same time, present the 

 greatest difficulties to study. Composed for the most part of soft beds, 

 they suffered extensive denudation, during the interval between the close 

 of the Carboniferous and the beginning of the Tertiary, during which 

 time they were, for the most part, exposed above the level of the sea ; by 

 the deposit of the great Tertiary series they were concealed, over immense 

 areas, and where they have been again exposed by the denudation of the 

 Tertiary, they have again suffered destructive denudation. At present, the 

 exposures are poor and unsatisfactory, rendering very difficult the determi- 

 nation of the relations of the different beds and the vertical extension of the 

 series. Mr. Smith, who has best studied these deposits, is of the opinion 

 that their total thickness is not less than 2,000 feet, and, although the data 

 for this calculation is very defective, I cannot say that it is exaggerated. 



The horizontal extension is more easy to determine. On the Tapajos 

 the rocks of this series appear at intervals, from a point just below the rapids 

 to near the village of Aveiros, a distance of about eighty miles. It is pos- 

 sible that they extend still farther north to near the mouth of the Tapajos, 

 since I am credibly informed that, near Santarem, a bed of limestone occurs, 

 which is most probably of Carboniferous age. To the westward of the 

 Tapajos, they have been recognized by Chandless on the Mauhe-assu, a 

 small river between the Tapajos and Madeira, and I consider it probable 

 that they extend as. far west as the latter river. I have information that 

 leads me to believe that thev exist to the eastward, on the Xingu, and I 



